1. Field of the Invention
This invention relates to cutting tools used for working hard or refractory materials. More particularly, the invention relates to an improvement in drill bits of the type having sintered diamond or boron nitride cutting edges, and a method of making the improved bits.
2. Description of Background Art
Cutting tools used to work hard or refractory materials have a relatively short life. Also, tools such as drill bits used in drilling or forming composites containing boron or carbon fibers used in the aircraft industry, as well as in other industries requiring high-strength, light-weight materials, experience rapid wear. Even the drilling of aluminum alloy engine blocks rapidly wears out steel drill bits.
In an effort to increase the wear resistance and life of steel twist drill bits used in applications of the type described above, as well as in the fabrication of such materials as fiberglass impregnated epoxy printed circuit boards, the tips of the bits are typically fabricated from a very hard substance such as tungsten carbide. However, even tungsten carbide is abraded fairly rapidly by composites such as printed circuit boards containing glass fibers. Thus, the bits must be re-sharpened or re-pointed relatively frequently, and eventually wear out. Therefore, even though tungsten carbide tipped drill bits last longer than all-steel bits, the downtime associated with re-sharpening and replacing carbide tipped drill bits is still a problem.
In an effort to further increase the life of drill bits used to work refractory materials, bits having harder cutting surfaces consisting of diamond or cubic boron nitride have been developed. One class of bits of this type has veins of polycrystalline diamond (PCD) or boron nitride (PCBN) material formed in the bit. Bits of this type generally employ grooves cut into a steel or tungsten carbide blank. Fine grains of PCD are packed into the grooves, and then subjected to great heat and pressure. This process causes the diamond grains to fuse to one another and to the carbide walls of the groove, thereby forming veins of hardened material. Drill bits of the type discussed above are disclosed in the following U.S. Pat. Nos.: